Calcium in the Spotlight

Not too long ago, calcium was the least controversial dietary supplement. Millions of people take the mineral calcium, hoping to keep their aging bones strong and prevent osteoporosis-related fractures, which half of all women eventually experience, as do many older men. The main debates were about which form of calcium is best, whether the pills could cause kidney stones and what other nutrients, if any, the supplements should also contain.

However, studies published in the past few years have probably made many people wonder if they should stop taking the pills. First, some studies have linked calcium pills to increased risk of heart disease. And in 2012, the influential U.S. Preventive Services Task Force dropped a bombshell when its draft recommendations concluded that standard doses of supplemental calcium and vitamin D don’t prevent fractures in postmenopausal women. Here's what you need to know.

Calcium and bones. Bones are living, active tissue and calcium is vital for bone health. (Calcium is also needed for many other bodily functions, such as regulating heartbeat and blood pressure, conducting nerve impulses, allowing muscles to contract and helping blood clot.) Bones constantly absorb and release calcium and other minerals, depending on many factors, such as hormones, exercise, genetics and overall diet. From childhood through early adulthood, bones grow in length and width, but then, in middle adulthood, the rate of bone loss exceeds that at which it is made.

Getting adequate calcium from childhood through early adulthood is important for bone health. Some studies have found that consuming calcium in adulthood leads to greater bone density and/ or reduced fracture risk, but others have not. Many factors affect bone health—from genetics, weight-bearing exercise and body size to age at menopause and a wide array of nutrients—so it’s hard to calculate calcium’s effect. And once an older adult has lost bone mass, increasing calcium intake by itself is not likely to have a big effect.

In its 2010 guidelines on calcium, which relate primarily to bone health, the Institute of Medicine (IOM) set the recommended dietary allowance (RDA) for women over 50 and men over 70 at 1,200 milligrams a day from food (preferably) and supplements, and for other adults at 1,000 milligrams. However, research suggests that 800 milligrams a day is enough for many healthy people, particularly those with adequate vitamin D intake and a diet rich in produce and whole grains.

It’s better to get calcium from food than supplements because foods naturally rich in calcium supply many nutrients important for bones and general health. Dairy foods are the leading sources of calcium, though many people have trouble digesting the lactose (milk sugar) in them. Fish with bones, such as sardines and canned salmon, as well as dark leafy greens and most tofu, contain good amounts. And there are lots of calcium-fortified products. However, many people don’t eat calcium-rich foods often, which is why supplements have been recommended to make up for the shortfall.

Calcium and heart disease. In recent years, several studies and one analysis of earlier research have suggested that calcium supplements modestly increase the risk of heart attacks. These clinical trials have had serious methodological flaws, however. For one thing, most were not designed to look at the effect of calcium on heart health.

In 2012, a widely reported observational study of 24,000 Germans, published in the journal Heart, concluded that the risk of heart attack doubled in people taking calcium supplements (but not with dietary calcium). The records on supplement use in this study were inadequate, however, and the number of calcium takers who had heart attacks was small, rendering the conclusions questionable.

Keep in mind that many other studies have not found a link between calcium pills and increased coronary risk. And some have suggested that higher calcium intakes reduce the risk of heart disease.

Still, despite their limitations, the negative studies raise concerns that require further research. Some researchers suggest that it's the high doses taken in concentrated form (often on an empty stomach) that makes the supplements at potential problem.

As for the concern that calcium from food or supplements can build up in coronary arteries and cause atherosclerosis, a 2013 analysis from the long-running Framingham Offspring Study concluded that people who consume the most calcium from food and/or supplements, as much as 3,000 milligrams a day, do not have more coronary calcium.

More reassuring news: A large Canadian study published in the Journal of Clinical Endocrinology & Metabolism in 2013 found that women who took up to 1,000 milligrams of calcium a day had a 22 percent lower death rate over a 10-year period than nonusers. There was no statistically significant effect on mortality rates in men or with higher doses of calcium.

Weight control. Some small studies over the years have suggested that calcium promotes weight control, but in 2009, a large, well-designed, two-year clinical trial found that 1,500 milligrams a day did not help.

Colon cancer. The weight of evidence suggests that calcium helps lower the risk of colon cancer, notably by reducing precancerous polyps. A review article in Nutrition Research Reviews in 2008, for instance, found that a high intake of dairy products, especially milk, was also associated with a reduced risk of colon cancer, probably because of their calcium, vitamin D, and other nutrients. And according to a 10-year AARP study in 2009, people who get the most calcium from dairy products and supplements are 20 percent less likely to develop colon cancer than those with a low intake.

Adequate calcium intake may also prevent the recurrence of colon cancer. In 2007, in the Journal of the National Cancer Institute, researchers found that people with colorectal adenomas (a type of precancerous polyp or growth) who took 1,200 milligrams of calcium daily reduced the risk of a recurrence of such polyps.

The task force weighs in

In 2012, an expert panel, part of the Preventive Services Task Force that advises the government on medical matters, concluded with “moderate certainty” that standard daily doses of calcium (1,000 milligrams) and low doses of vitamin D (400 IU or less) do not prevent fractures in postmenopausal women without osteoporosis. Thus it advised such women not to take the supplements.

Because it said the evidence is inadequate, the panel did not pass judgment on higher doses of vitamin D (combined with calcium) for fracture risk, nor did it discuss younger women, men, people with osteoporosis, or those living in nursing homes. It took note of the small increased risk of kidney stones from calcium, but did not mention coronary risk.

Many researchers have raised objections to the draft guidelines, saying the task force has misinterpreted the research or at least put too negative a spin on it. In particular, critics have questioned the focus on low-dose vitamin D, since there’s a growing consensus that higher doses are needed for bone health. The task force itself stated that 400 IU “would not be considered sufficient today.” Moreover, the research analysis that was prepared for the task force concluded that “combined vitamin D and calcium supplementation can reduce fracture risk, but the effects may be smaller among community-dwelling older adults than among institutionalized elderly persons.”

To add to the confusion, in 2012 another task force panel recommended vitamin D supplements to prevent falls in older people, which are the leading cause of fractures.

How much calcium is too much?

High doses of calcium supplements (especially when taken without food) are known to increase the risk of certain kinds of kidney stones. In contrast, foods naturally rich in calcium (notably dairy products) seem to protect against kidney stones.

Largely because of concerns about excessive blood levels of calcium, the IOM has set the upper limit at 2,500 milligrams of calcium a day (from food and supplements) for those under 50, and 2,000 milligrams for older people. If you eat a lot of dairy and calcium-fortified foods and also take a supplement, you may be getting up to that level. In fact, the IOM warned that some women over 50 are actually taking too much supplemental calcium on top of what they get from food. There’s no reason to consume that much calcium, unless your doctor has advised it because you have osteoporosis or certain other medical conditions. If you’re prone to stones, check with your doctor before taking any calcium pills.

What to do about calcium

We still advise taking calcium and vitamin D supplements if you don’t get enough from food. Keep in mind:

Get as much calcium as you can from foods—along with other bone-healthy nutrients. If your diet is good, you probably don’t even need to consider supplements. Add up your food sources (see chart below, and check labels on foods). You may be consuming more than you think.

Take 800 to 1,000 IU of virtamin D, or higher amounts if appropriate.

Don’t expect calcium intake to have a big effect on bone health once you’re past middle age and have lost bone mass. Still, calcium supplements plus adequate vitamin D may play a small beneficial role in people over 50, especially in those with low dietary intakes. And every little bit helps when it comes to bone health.

If you take a calcium supplement, look for the most convenient and cheapest form. That’s usually calcium carbonate.

To err on the side of caution, don’t exceed 1,000 to 1,200 milligrams of supplemental calcium a day. On days when you eat lots of calcium-rich foods, reduce or skip the supplement. Or take only 200 to 300 milligrams (if you have 500 or 600 milligram tablets, you can cut one in half).

If you take thyroid hormones, corticosteroids, tetracycline, or iron pills, check with your doctor or pharmacist before taking calcium supplements. Calcium can interfere with these and some other drugs and minerals. On the other hand, reflux drugs—H-2 blockers (such as Zantac or Pepcid) and proton pump inhibitors (such as Nexium or Prilosec)—decrease calcium absorption, so you may need a higher calcium intake. People with certain disorders, such as celiac disease, also have decreased calcium absorption and may need supplements.

Calcium: supplemental advice

Calcium naturally occurs bound to other substances—such as carbonate, citrate or gluconate—never alone. Each form contains a different percentage of “elemental” calcium. Calcium carbonate contains the most calcium by weight—40 percent. The more calcium, the fewer pills you need. Some studies have found that calcium citrate is best absorbed. Calcium carbonate is cheapest, and one pill typically supplies 500 or 600 milligrams of elemental calcium. Some other forms provide much less calcium per pill.

There’s little added benefit from taking calcium in doses greater than 500 milligrams at a time, since the body absorbs larger amounts less efficiently. It’s best to spread your calcium intake throughout the day, if possible—which is another reasonfood sources are preferable. Try to take calcium carbonate with meals, since stomach acid secreted during digestion helps enhance its absorption. Calcium citrate is well absorbed without stomach acid, so you can take it anytime.